Faster dieback of rainforests altering tropical carbon sinks under climate change

Tropical regions are home for 45% of the world’s forested landmasses, which comprises approximately 15% of global land areas. Among them tropical rainforest encompasses around 25% of all the ecological zones, which are spread largely in South America, Central America, Africa, and Southeast Asia. They are the home for two-thirds of the terrestrial biomass and act as natural carbon sinks by exchanging more carbon fluxes with the atmosphere compare to any other biomes in the world. Carbon sinks in the tropical rainforests are restricting the global warming to attain unprecedented heights. The carbon content of soil is about three times higher than that of atmosphere or vegetation, which makes soil respiration as the largest contributor of carbon efflux into the atmosphere through root (autotrophic) and microbial (heterotrophic) respiration. However, deforestation and climate change is switching them to a net carbon source at some of the deforested patches. Using machine learning algorithm we predict that more than 50% of the tropical rainforests will undergo rapid “Savannisation”/transformation by the end of 21^st century under high emission scenarios. Climate change projects ‘El Niño-like’ warming condition, which decreases precipitation in the rainforests and favors atmospheric dryness. These transformations in vegetation morphology underpins the higher probability of occurrences of Net ecosystem production (NEP) i.e. the differences between Gross Primary Productivity (GPP) and Respiration (RE) less than 0, due to increasing microbial activity in the degraded patches of Central Amazonia, Central America (Nicaragua, Honduras, Mexico), Western Africa (coastal Ghana, Benin, Togo, Nigeria) and South East Asian (Greater Sunda islands) rainforests, and thereby transform the traditional carbon sinks into a net source of carbon to the atmosphere. These transformations are more acute in the Amazonian and Central American sectors of the rainforests, which is expected to accelerate by the middle of 21^st century. This is due to faster degradation of rainforests if global mean temperature warms beyond 2.3^◦K (by late 2050’s) and will undergo total transformation if warming exceeds 3.8^◦K (by ~2075). In Central Amazonia vegetation degradation saturates the carbon sink and more than 25% of the rainforests will transform into a net carbon source due to increase in soil microbial respiration. This alteration will exacerbate global warming and has consequences for policies that are intended to stabilize Earth’s climate.